The present invention relates to data storage devices and, in particular, to a method of encoding servo information on discs and hard disc drives manufactured using the same.
A typical disc drive storage system includes one or more magnetic discs which are mounted for co-rotation on a hub or spindle. A typical disc drive also includes a transducer supported by a hydrodynamic bearing which flies above each magnetic disc. The transducer and the hydrodynamic bearing are collectively referred to as a data head. A drive controller is conventionally used for controlling the disc drive based on commands received from a host system. The drive controller controls the disc drive to retrieve information from the magnetic discs and to store information on the magnetic discs. An electromechanical actuator operates within a negative feedback, closed-loop servo system to move the data head radially or linearly over the disc surface for track seek operations and holds the transducer directly above a desired track or cylinder on the disc surface for track following operations.
Information is typically stored in concentric tracks on the surface of the magnetic discs by providing a write signal to the data head to encode flux reversals on the surface of the magnetic discs representing the data to be stored. In retrieving data from the discs, the drive controller controls the electromechanical actuator so that the data head flies above the desired track or cylinder on the magnetic discs, sensing the flux reversals on the magnetic discs, and generating a read signal based on those flux reversals.
In an embedded servo-type system, servo information (for example in the form of servo bursts) is recorded on data tracks which also contain stored data. The servo bursts are typically temporally spaced evenly about the circumference of each data track. Data is recorded on the data tracks between the servo bursts. In a dedicated servo-type system, an entire disc surface in a disc drive is dedicated to storing the servo information, while other disc surfaces are used for data storage.
As the data head reads the servo information, the transducer provides a position signal which is decoded by a position demodulator and presented in digital form to a servo control processor. The servo control processor essentially compares actual radial position of the transducer over the disc (as indicated by the embedded servo burst) with a desired position and commands the actuator to move in order to minimize position error.
Often, the servo information is prerecorded on the disc surfaces during manufacture of the disc drive module using a process sometimes referred to as servo writing. Each disc drive module is mounted to a servo writer support assembly which precisely locates the disc surfaces relative to a reference or origin. The servo writer support assembly supports a position sensor, such as laser light interferometer, which detects the position of the actuator relative to the disc surfaces. The position sensor is electrically inserted within the disc drive""s negative feedback, closed-loop servo system for providing position information to the servo system while the servo data is being written to the disc surfaces. The servo writer support assembly may also support a clock writer transducer which writes a clock pattern onto the disc surface which is used for temporally spacing the servo data about the circumference of each track.
Using a servo writer support assembly to write servo information typically requires many minutes for each disc assembly. Such time slows manufacturing throughput and potentially increases the cost of the finished product. Another limitation is that the servo written patterns generally consume about 5-10% of the usable recording area in a given disc drive.
Another technique for writing servo information uses the disc drive itself to write the servo information in situ. In Situ recording means that the servo patterns are recorded on a fully assembled drive using the product head. An example of this technique is set forth in U.S. Pat. No. 5,875,064, to Chainer et al. However, one limitation that has generally limited self-servowriting techniques is that disturbances inherent in the drive itself, such as disc flutter and spindle non-repeatable runout (NRRO), limit the radial and circumferential accuracy of the position sensing pattern. As a result, the limits of pure in situ techniques are not known.
Buried magnetic recording has been considered in hard disc systems to increase the usable recording area on the disc surfaces. See, for example, U.S. Pat. Nos. 5,055,951 and 4,318,141. These techniques use thick magnetic media and a magnetic recording head to write servo information deep into the data storage layer. The data signal is then written into the shallow part of the data storage layer without completely erasing the servo information which has been recorded deeper into the layer. This partial penetration magnetic recording introduces the potential to compromise the user data.
As industry continues to press disc drive manufacturers to provide disc drives with increased storage capacity at lower costs, it is becoming increasingly important to provide disc drives with increasing track densities while minimizing manufacturing time and labor costs.
The present invention addresses these and other problems, and offers other advantages over the prior art.
The present invention relates to data storage systems having magnetic servo information and magnetically stored data on the same disc which solves the above-mentioned problems.
A data storage system includes a data storage disc for storing magnetically encoded data and servo information. The data storage disc includes a data layer adapted to be magnetically encoded with data to be written to the data storage disc, and a servo information layer formed beneath the data layer and having magnetic servo pits formed therein to provide servo information. The magnetic servo pits are positioned in portions of the servo information layer which are at least partially directly beneath magnetically encoded data regions on the data layer such that a data head can read both magnetically stored data and servo information from the disc at substantially the same time.
The invention also includes a method of manufacturing a data storage disc having servo pits in a servo information layer directly beneath magnetically encoded data stored on a data layer.
These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.